The invention relates to a spun-bonded nonwoven fabric made of polyolefin filaments having a titer<1.6 dtex. The spun-bonded nonwoven fabric is characterized by special barrier properties.
The invention further relates to the manufacture of a laminate using the spun-bonded nonwoven fabric according to the invention, and use of the spun-bonded nonwoven fabric and use of the laminate manufactured using the spun-bonded nonwoven fabric.
Nonwoven fabrics are textile fabrics which may be manufactured in various ways. In addition to wet nonwoven fabric and dry nonwoven fabric manufacture, a distinction is made between melt spinning and melt blowing (melt-blown technology). The two technologies, melt spinning and melt blowing, have the advantage that the plastic granules may be directly converted to the finished fabric using an appropriate manufacturing unit. This is the basis for the comparatively high productivity of these units in nonwoven fabric manufacture.
In melt spinning, polymer granules are melted in an extruder, pressed through the openings (referred to as spinnerets) in a spinning plate, and after cooling are pneumatically or mechanically drawn. The drawing process determines the final strength of the filaments. After drawing, the filaments are deposited loose on a moving laydown belt, and in the region of the contacting intersection points are chemically or thermally bonded to produce so-called interlacing points. With increased bonding, the softness of the nonwoven fabric thus formed decreases and its flexural strength increases. Multiple superposed spun-bonded nonwoven fabric layers which are the same or different may be thermally bonded, for example by calendering, to produce a composite material (laminate).
The productivity is lower for melt blowing than for melt spinning. As a result, the nonwoven fabrics produced by melt blowing (melt-blown technologies) have a lower mechanical load capacity than those produced by melt spinning. In comparison to melt spinning, however, melt blowing is technically more complex and therefore more costly.
The aim of low-cost nonwoven fabric manufacture, therefore, is to replace, or, for laminate manufacturing, to reduce, the nonwoven fabrics produced by melt blowing by nonwoven fabrics which ideally have been produced completely by melt spinning. However, this first requires that the barrier properties of the layers produced by melt spinning be significantly improved.
The barrier properties of a nonwoven fabric are characterized, among other factors, by its air permeability and waterproofness. The measure for the waterproofness is the water pressure, expressed in mbar or in cm of a water column, at which the first water droplets penetrate the test material at the third location on the test surface.
Various other measures are known from the prior art for improving the barrier properties of the nonwoven fabrics produced by melt spinning. In addition to coating the melted spun-bonded nonwoven fabrics and applying films for improving the barrier properties, these measures include above all the use of bicomponent fibers, for example core/sheath fibers or splittable fibers. Coatings or films disadvantageously result in additional raw material and manufacturing costs. The coatings or films may also adversely affect the breathability. The disadvantage of the bicomponent fibers is their high cost.
In addition, increasing the basis weight and using fibers with a greater degree of fineness are known measures for improving the barrier properties of spun-bonded nonwoven fabrics.
U.S. Pat. No. 5,885,909 describes a spun-bonded nonwoven fabric having fibers with a fineness of 1 denier or less and characterized by a Frazier air permeability of at least 70 m3/(m2·min) and a water column of at least 15 cm. The essence of the invention lies in the teaching that the pore size and thus the air permeability and waterproofness of the melt-spun nonwoven fabric produced from the filaments may be influenced by the filament hardness and the fineness of the filaments.